This application is a continuation of Application No. 101 10 282.8 filed in Germany on Mar. 2, 2001, to which this application claims priority under 35 U.S.C. xc2xa7119 and/or 365.
The present invention relates to a planet gear comprising a planet carrier rotatable around an axis of rotation, at least one planet wheel arranged on the planet carrier, a sun wheel and a ring gear, wherein the planet wheel is arranged movably at least radially with respect to the axis of rotation of the planet carrier.
A planet gear of this type is known from DE 195 46 586 and from EP 0 779 449. The radial movability of the planet wheels with respect to the planet carrier effects in the known planet gear a significant increase of the life, which is obviously a result of the fact that static over definitions are avoided. However, it proved that the demands on the planet gear are not only the demand for a longer life but also that freedom from backlash is increasingly required in particular for certain applications
Thus, it is the object of the present invention to design a planet gear of the above-mentioned kind in a manner that as little backlash as possible occurs.
For this purpose, the invention provides that the ring gear is formed in two pieces on a plane perpendicular to the axis of rotation of the planet carrier, wherein the two halves of the ring gear can be rotated against each other and thereby effect a radial shift of the planet wheel in the direction towards the sun wheel in order to reduce backlash.
Planet gears with divided ring gears are known per se. For this purpose, reference is for instance made to DE 37 38 607 A1. The multi-step planet gear that is known there also has divided planet wheel besides having a divided ring gear. By rotating the halves of the ring gear against each other by means of adjusting screws, the two planet wheels are positioned against each other so that a possible backlash between the ring gear and the planet wheels is avoided. However, the disadvantage thereof is that in one direction of rotation only one half of the tooth flanks of the sun wheel perform the carrying work. If it is intended to transfer the same power by this gear as transferred by a conventional planet gear, the axial overall length of the gear is compulsorily increased. In contrast thereto, the gear according to the present invention provides that only the ring gear is divided but not the planet wheels. Instead, the planet wheels are supported in a radially movable manner so that when rotating the ring gear halves, not only the backlash between the planet wheel and the ring wheel is reduced, but the backlash between the sun wheel and the planet wheel is also reduced due to the radial shift in the direction towards the sun wheel. It is advantageous that the tooth flanks of the sun wheel carry across the sun wheel""s entire axial length so that despite the reduction of backlash, the overall dimensions of the planet gear do not have to be changed.
According to an embodiment of the invention, the two ring gear halves can be fixed against each other. This may for instance be carried out in that the one half of the ring gear is fixed in the housing, whereas the other half of the ring gear can be rotated by means of an adjusting screw against the fixed half of the ring gear until the desired freedom from backlash is achieved.
Another embodiment provides that the two ring gear halves are spring-elastically positioned against each other in the tangential direction. For this purpose, the one half of the ring gear may again be fixed in the housing, whereas the other half of the ring gear is arranged rotatably with respect to the fixed half of the ring gear, and this other half of the ring gear is supported by a spring supported at the housing. The strength of the spring will be chosen in accordance with the dimensions of the gear and the torques to be transferred.
An especially preferred embodiment provides a combination of a spring-elastic pre-positioning of the two halves of the ring gears and their subsequent relative fixing. For this embodiment, the springs positioning the two halves of the ring gear against each other are merely required for a freedom from backlash being produced e.g. during idle running or in the case of a very small load. Then, the two halves of the ring gear are fixedly positioned against each other, e.g. by means of a screw, so that the springs do not have to transfer a torque.
According to a preferred embodiment, the two halves of the ring gear may be connected to one another through a train of gears in a manner that an axial movement of an element of the train of gears effects a rotation of the two halves of the ring gear against each other. Such a train of gears, which may for instance be a tapered gear, would have the advantage that the freedom from backlash could be adjusted from a front side of the gear. This is in particular of advantage if in the installed condition of the gear the backlash must be re-adjusted and the radial accessibility of the gear is not ensured.
An especially simple train of gears can be realized if at least one of the two halves of the ring gear is axially movable with respect to the other half of the ring gear. Then, the axially movable half of the ring gear may be connected via a tapered gear with the axially and tangentially fixed half of the ring gear so that an axial shift of the movable half of the ring gear effects a mutual rotation of the two halves of the ring gear.
Such a coupling of the halves of the ring gear via a train of gear is particularly advantageous if the trains of gear of the halves of the ring gear of several gear steps are connected to one another. Then, all gear steps of the planet gear can be adjusted in a manner free from backlash by one single operation of the train of gears.
A preferred embodiment of the invention provides that the two halves of the ring gear of the planet gear can be positioned in the axial direction, wherein the two halves of the ring gear are connected to one another in the tangential direction via a spring, which effects a mutual rotation of the two halves of the ring gear in the axial non-positioned condition of the two halves of the ring gear. As mentioned above, the strength of the springs is chosen in a manner that after releasing the fastening screws, the two halves of the ring gears rotate against each other so that the planets are shifted radially until a compensation of backlash is obtained. After reaching this backlash compensation, the axial fastening screws are fastened so that the two halves of the ring gear can be fixed against each other. In this state free from backlash, the springs do not transfer a load. The strength of the springs must therefore not be adapted to the torque to be transferred by the gear.
A solution especially easy to realize provides that the halves of the rings gear are connected to one another via at least one fastening screw arranged on a parallel axis of rotation which penetrates the halves of the ring gear, wherein in at least one half of the ring gear the bore for the screw has backlash in the tangential direction of the ring gear in a manner that the half of the ring gear may move tangentially with respect to the screw. That means that the screw can be fixed tangentially in one half of the ring gear, wherein the other half of the ring gear has a bore with a tangential backlash so that the two halves of the ring gear can be slightly rotated against each other. Since the backlash to be eliminated in the gear is usually not very grerat, a relatively small difference in dimension between the bore and the outer diameter of the fastening screw is sufficient.
In a structurally particularly simple manner, the spring provided for the rotation of the halves of the ring gear against each other can be arranged, in which a recess opening into the bore for accommodating a pressure spring is provided in the movable half of the ring gear, said pressure spring being radially supported against the screw.
In a multi-step planet gear it is favourable if all halves of the ring gear are penetrated by the fastening screw.
In particular when higher torques are to be transferred by the gear, it is also of advantage if at least two diametrally opposing fastening screws are arranged.